Synthesis of large-sized monodisperse polystyrene microspheres by dispersion polymerization with dropwise monomer feeding procedure

Highly monodisperse polystyrene (PS) microspheres in the size range of 3.75–7.09 μm were synthesized by dispersion polymerization with dropwise monomer feeding procedure. The morphology, size, and particle size distribution (PSD) of the PS microspheres obtained by different monomer feeding modes, including batch polymerization and various feeding rates, were investigated. The PSD of particles showed a close dependence on feeding rate. The PS microspheres with low coefficient of variation (CV) values all less than 4.8% obtained by the optimum feeding rates revealed better uniformity than those by batch polymerization (CV values all more than 8.2%). According to the time courses of monomer conversion and particle numbers, the effects of monomer feeding modes on the polymerization reaction of the large-sized PS microspheres were clarified. It is found that the dropwise monomer feeding procedure is promising for the synthesis of large-sized monodisperse PS particles in 3.75–7.09 μm.     

Synthesis of multifunctional macroporous-mesoporous TiO<Subscript>2</Subscript>-bioglasses for bone tissue engineering

Hierarchical porous TiO₂-bioglasses (TiO₂-BGs) with the macropore with the size of 30–50 μm and the mesopore with the diameter of 4.4–5.6 nm have been synthesized through the evaporation-induced self-assembly method. The corn stalks were used as the macroporous template and P123 as the mesoporous template in the process. The chemical and physical properties of the hierarchical porous TiO₂-BGs before and after immersion in simulated fluid (SBF) were evaluated by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption, and Energy dispersive spectrometer. The effect of TiO₂ content on the formation of surface hydroxyapatite and drug release profiles of the fabricated TiO₂-BGs in SBF were investigated in detail. It was found that macroporous-mesoporous TiO₂-bioglasses (MM TiO₂-BGs) exhibited a good ability of surface hydroxyapatite formation comparing with macroporous-mesoporous bioglasses. It took only 3 h for the MM TiO₂-BGs to be covered with the hydroxyapatite layer. It can be ascribed to the present of Ti–OH which may improve the spontaneous growth of apatite by consuming the calcium and phosphate ions from SBF. Additionally, MM TiO₂-BGs also showed good drug sustained release profiles. Therefore, the multifunctional MM TiO₂-BGs reported here could be a good candidate for application in bone tissue engineering.     

Combination of microspheres and sol-gel electrophoresis for the formation of large-area ordered macroporous SiO2

A simple and effective fabrication scheme involving sequential electrophoretic depositions of polystyrene (PS) microspheres (500 nm and 1 μm in diameter) and SiO₂ sols (~ 5 nm in diameter) to produce large-area ordered macroporous SiO₂ inverse opals (2 × 2 cm²) on ITO substrates is demonstrated. The zeta potentials for PS microsphere suspension and SiO₂ sols are measured to determine an optimized processing window in which both samples carry negative surface charges and sol-gel transformation can be properly implemented. Our approach entails the electrophoresis of PS microspheres to render a colloidal crystal with negligible defects. Afterward, SiO₂ sols are infiltrated to the interstitial voids among the closely-packed PS microspheres via another electrophoresis process, followed by an oxidation treatment to remove the PS colloidal template and complete the densification of SiO₂ gels. The resulting SiO₂ inverse opals reveal impressive surface uniformity and structural integrity. Fourier transform infrared spectroscopy confirms the complete removal of PS microspheres, leaving an intact SiO₂ skeleton, whereas X-ray diffraction pattern indicates its amorphous nature.     

A co-templated approach to hierarchically mesoporous–macroporous bioactive glasses (MMBG) scaffolds for bone tissue regeneration

In this paper, one kind of well-ordered hierarchical mesoporous–macroporous bioactive glasses (MMBG) scaffolds with large pore size of 60–120 μm and mesoporous phase in inner-wall has synthesized successfully. This method used stem core of corn as macroporous template and P123 as mesoporous template. The final samples have replicated the structure of the macroporous plant templates precisely. Since the aperture and pore structure of different plants are variable, it provides a possible way for the synthesis of materials with various aperture holes and pore structure. The organizational structure of final sample is benefit to transport and storage guest molecule, making these hierarchical porous materials have more superior performance and application in the field of macromolecules separation, bone tissue regeneration, and drug delivery, etc. The in vitro tests indicated hierarchical MMBG scaffolds have well capacity for inducing the HA growth. They have the potential to satisfy the demands of bone tissue engineering regeneration.     

Preparation of hollow silica microspheres with controlled shell thickness in supercritical fluids

This article presents a novel route to prepare hollow silica microspheres with well-defined wall thickness by using cross-linked polystyrene (PS) microspheres as templates with the assistance of supercritical carbon dioxide (SC-CO₂). In this approach, the cross-linked PS templates can be firstly prepared via emulsifier-free polymerization method by using ethylene glycol dimethacrylate or divinylbenzene as cross-linkers. Then, the silica shell from the sol–gel process of tetraethyl orthosilicate (TEOS) which was penetrated into the PS template with the assistance of SC-CO₂ was obtained. Finally, the hollow silica spheres were generated after calcinations at 600 °C for 4 h. The shell thickness of the hollow silica spheres could be finely tuned not only by adjusting the TEOS/PS ratio, which is the most frequently used method, but also by changing the pressure and aging time of the SC-CO₂ treatment. Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscope were used to characterize these hollow silica spheres.     

Hydrothermal synthesis of 2D ordered macroporous ZnO films

The ZnO films with two-dimensional ordered macroporous structure were successfully fabricated through hydrothermal crystal growth of ZnO on the ZnO substrate covered with a monolayer of polystyrene (PS) spheres as template. The precursor solution of hydrothermal crystal growth of ZnO were prepared by equimolar solution of Zn(NO₃)₂·6H₂O and hexamethylenetramine (HMT). The confinement effect of the PS spheres template on the growth of ZnO nanorods and the influence of sodium citrate on the crystal growth of ZnO had been studied. The film surface morphology and the preferential growth of ZnO crystal were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Also, the photoluminescence spectrum of ZnO films had been measured, and the corresponding mechanism was discussed. __________ Translated from Chemistry, 2007, 70 (8): 587–592 [译自: 化学通报]     

Silica covered porphyrin microstructures obtained in sol–gel processes

In this article, we report on the formation of well-defined highly emissive silica-covered porphyrin microstructures in base-catalyzed sol–gel processes. The microstructures were obtained by self-assembly of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (mTHPP) at room temperature. Tetraethoxysilane (TEOS) was used as a silica precursor. The hybrid mTHPP- silica particles were characterized by means of reflectance UV–Vis and microscopy techniques including atomic force microscopy, scanning electron microscopy (SEM) and confocal fluorescence microscopy (CM). The SEM and TEM observations revealed that depending on the porphyrin concentration used in the synthesis, the shape of the hybrid mTHPP-silica particles has changed from ribbon-like (c _mTHPP = 2.09 mM) to rhombus-like structures (c _mTHPP = 4.35 mM). The ribbons were straight-edged, uniform in width (1.2–1.8 μm) and height (350–400 nm), and variable in length (40–100 μm). The rhombs were 1–3.7 μm in height, 7–25 μm in length, and 3.5–15 μm in width, and the ratio of length to width was uniform and equal to ca. 1.8–2. UV–Vis absorption spectra indicated that the J-aggregates and H-aggregates formed in the systems with lower and higher porphyrin content, respectively. Formation of different type of porphyrin aggregates in both systems resulted in different emission spectra, as it was shown with CM.     

Terrace formation with a picoliter sol–gel droplet for spherical cavity Raman laser

We have successfully made terrace-microspheres for laser emission: micrometer-size spherical cavity laser having terrace-shaped pumping-light entrance. Organic–inorganic hybrid materials in the binary system of 3-methacryloxypropyltrimethoxysilane (MOPS) and tetramethoxysilane (TMOS) were used for preparing the terrace on glass microspheres by sol–gel technique. To make terrace portion, a picoliter sol was supplied with a micro-capillary suppliers into the bottom of spheres and subsequently the terrace-shaped sol was solidified. In the MOPS-TMOS binary system, essential sol properties such as viscosity change and sol–gel transformation rate determine the terrace structures. Compositions and volumes of the sol remarkably influenced viscosity increase and subsequent solidification. In this study, we showed that the control of the terrace structure for spherical cavity Raman lasers was possible by choosing the suitable compositions of picoliter-volume sol droplets. Terrace-microspheres from high-refractive-index glass spheres (n _D  = 1.93) was pumped with a CW Ar⁺ laser (514.5 nm wavelength), and stimulated Raman emission was demonstrated above the threshold of 2.5 mW.     

Electrophoretic sol–gel synthesis of SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> nanowires

We report the independent invention of perovskite ferroelectric nanowires strontium bismuth tantalate (SrBi₂Ta₂O₉, SBT). Electrophoretic sol–gel techniques have been used successfully. The morphology and structures are analyzed via SEM, TEM and XRD. SBT nanowires and nanoparticles filled template revealed 30 and 40 μm long, respectively. SBT are proved to be a single phase of orthorhombic perovskite structure. As it indicated, SBT nanowires has been crystallized at 700 °C. To minimize surface polarity, SBT nanowires oriented preferentially along the growing axis (c axis) by translation and rotation of atomic clusters of SBT.     

漂浮法制备SiO2有序大孔材料

用漂浮组装方法以亚微米尺度单分散的聚苯乙烯(PS)微球作为模板, 在悬浮液气-液界面处组装PS模板微球与纳米级胶体颗粒, 形成二元胶体颗粒共混物, 再去除模板得到有序大孔材料.     

Molecularly imprinted polymer based on chemiluminescence imaging for the chiral recognition of dansyl-phenylalanine

A new molecularly imprinted polymer (MIP)–chemiluminescence (CL) imaging detection approach towards chiral recognition of dansyl-phenylalanine (Phe) is presented. The polymer microspheres were synthesized using precipitation polymerization with dansyl-l-Phe as template. Polymer microspheres were immobilized in microtiter plates (96 wells) using poly(vinyl alcohol) (PVA) as glue. The analyte was selectively adsorbed on the MIP microspheres. After washing, the bound fraction was quantified based on peroxyoxalate chemiluminescence (PO-CL) analysis. In the presence of dansyl-Phe, bis(2,4,6-trichlorophenyl)oxalate (TCPO) reacted with hydrogen peroxide (H₂O₂) to emit chemiluminescence. The signal was detected and quantified with a highly sensitive cooled charge-coupled device (CCD). Influencing factors were investigated and optimized in detail. Control experiments using capillary electrophoresis showed that there was no significant difference between the proposed method and the control method at a confidence level of 95%. The method can perform 96 independent measurements simultaneously in 30 min and the limits of detection (LODs) for dansyl-l-Phe and dansyl-d-Phe were 0.025 μmol L⁻¹ and 0.075 μmol L⁻¹ (3σ), respectively. The relative standard deviation (RSD) for 11 parallel measurements of dansyl-l-Phe (0.78 μmol L⁻¹) was 8%. The results show that MIP-based CL imaging can become a useful analytical technology for quick chiral recognition.     

Preparation and performances of carbon aerogel microspheres for the application of supercapacitor

Carbon aerogel (CA) microspheres were successfully synthesized by an inverse emulsion polymerization routine. Morphology and physical properties of the CA microspheres were characterized by scanning electron microscopy, N₂ sorption isotherm, and transmission electron microscopy. The results showed that the CA microspheres were all fine spheres with diameters about 4 μm, and the CA microsphere was a typical mesoporous material with ordered mesoporous nano-network structure. The maximum capacitance of the electrode obtained from cyclic voltammetry was 187.08 F/g and the capacitance of the supercapacitor resulted from galvanostatic charge–discharge tests was up to 45.98 F/g. The supercapacitor using CA microsphere as electrode material presented a long cycle life, high charge–discharge efficiency, and low R _s of 0.70 Ω in 6 M KOH electrolyte.     

(Ba<Subscript>0.93</Subscript>Nd<Subscript>0.07</Subscript>)TiO<Subscript>3</Subscript> thin films prepared by sol–gel method as a potential dielectric resonator antenna application

In this paper, we report the application of Neodymium (Nd) doped barium titanate thin films (Ba_1-xNd_x) TiO₃ with x = 0 and 0.07 as dielectric resonator antenna. The films were prepared using the sol–gel method and dip-coating technique. Barium acetate, titanium (IV) isopropoxide and neodymium (III) acetate hydrate were used as precursors while glacial acetic acid and acetylacetone were used as solvents. Si wafers were used as a substrate with dipping times varying from 10, 30, and 50 s. The 0.07 films were >800 nm thick and crystallized after being annealed at 800°C for 30 min. The films were tested as dielectric resonator antenna. It was found that, on the actual antenna circuit, the resonant frequency decreased as the (Ba_0.93Nd_0.07) TiO₃ films thickness increased (from 0.8379, to 5.4525 μm). All samples resonate in the range of 8.68–8.83 GHz with quasi omni-directional radiation patterns.     

Comparative study of the synthesis of KReO<Subscript>4</Subscript> using acrylamide sol–gel and solid-state reaction methods

KReO₄ was synthesized by solid-state reaction and for the first time by sol–gel method via acrylamide polymerization. X-ray diffraction analysis showed that a single phase of KReO₄ was obtained by both methods at 500–505 °C having a tetragonal unit cell. The solid-state reaction samples had a grain size of 5 μm and the sol–gel samples had fibrous aspect, agglomerated between 10 and 100 μm. By TEM it was observed nanocrystals of 100 nm, it is suggested that the xerogel fibers are formed by nanocrystals. From the results obtained, we concluded that the morphology is strongly influenced by the method of synthesis used.     

Sol–gel synthesis and crystallization behaviour of β-spodumene

Lithium aluminum silicate powders in the form of β-spodumene were synthesized through sol–gel technique by mixing boehmite sol, silica sol and lithium salt. The gel and oxide powders were characterized by thermogravimetry, differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy. DTA, XRD and FTIR results confirmed that crystallization of β-spodumene took place at about 800 °C. The tiny crystallites with average size less than 1 μm appeared when the gel powders were sintered at 800 °C. A substantial increase of the crystal grain size was observed with increasing sintering temperatures.     

Sol–gel preparation of highly transparent α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> film for the application in red color filter

α-Fe₂O₃ films as inorganic red color filter were synthesized through a simple procedure, epoxide assisted sol–gel route. The sol was prepared through reaction of FeCl₂ in boiling ethanol solution with propylene oxide. The films were formed by the dip-coating of sol on substrate, drying and the following annealing steps. The obtained α-Fe₂O₃ films were composed of homogeneous distributed α-Fe₂O₃ nanoparticles with size of 30–50 nm. The film shows strong absorption to the light below 600 nm and high transparency to the red light (87% at 630 nm). As inorganic red color filter, the optic behavior of this film is nearly as same as the organic color filter made of dye.     

Characterization of MoO3 nanorods for lithium battery using PVP as a surfactant

We synthesized MoO₃ nanorods using poly (vinyl pyrrolidone) (PVP) as a surfactant through the hydrothermal route for making a cathode for a lithium battery. Scanning electron microscopy images reveal the structures to have dimensions on the order of 1–10 μm in length and 50–200 nm in diameter. Analytical techniques such as X-ray diffractometry, Fourier transformation infrared spectroscopy, thermogravimetric analysis, and cyclic voltammetry were used to characterize the nanorods. The measured specific charge of MoO₃ nanorods prepared through a 15-day hydrothermal reaction was 156 mAhg⁻¹ during the initial discharge process.     

Bismuth titanate thin films prepared by wet-chemical techniques: effect of sol ageing time

In this work, layered perovskite bismuth titanate (Bi₄Ti₃O₁₂) thin films were fabricated on α-alumina substrates by spin coating process. Precursor sol was prepared by sol–gel process from bismuth nitrate and titanium butoxide in concentrated acetic acid, with diethylamine as a stabilizer. Processes occurring in the precursor sol were followed in the ageing period of 20 days. Thin films prepared from the as-synthesized and aged sols are crack-free, with the thickness of ~1 μm, uniform surface texture and rounded grains having grain size in nanometer range. Sintering of thin films was performed at various temperatures, and sintered thin films exhibited dense structure, fully crystallized with typical Aurivillius phase and without any preferred orientation and impurity phase. The influence of ageing of the precursor sol on the microstructure of obtained thin films was also investigated. Direct relation between hydrodynamic diameter of precursor particles and the morphology and the grain size of the obtained films was observed.     

Preparation of multilevel macroporous materials using natural plants as templates

A series of two-dimensionally (2D) ordered macroporous silica materials have been prepared by using eight natural plants as templates. The macroporous materials replicate the complicated morphologies of natural plants precisely, and retained the original pore shape of plants. Meanwhile, these macroporous materials showed roughly similar morphologies and pore structure by the same part of plants, while the distribution of macropore diameters is ca. 8–1,000 μm. It may provide a effective approach to prepare macroporous materials with different 2D pore and complicated morphologies. These 2D ordered macropore silica materials may have potentially application for tissue repairing and templates materials to produce other kinds of macropores or hierarchically porous materials.     

Investigation of Yeast Invertase Immobilization onto Cupric Ion-Chelated,Porous, and Biocompatible Poly(Hydroxyethyl Methacrylate-<Emphasis Type="Italic">n</Emphasis>-Vinyl Imidazole) Microspheres

Cupric ion-chelated poly(hydroxyethyl methacrylate-n-vinyl imidazole) (poly(HEMA-VIM)) microspheres prepared by suspension polymerization were investigated as a specific adsorbent for immobilization of yeast invertase in a batch system. They were characterized by scanning electron microscopy, surface area, and pore size measurements. They have spherical shape and porous structure. The specific surface area of the p(HEMA-VIM) spheres was found to be 81.2 m²/g with a size range of 70–120 μm in diameter, and the swelling ratio was 86.9%. Then, Cu(II) ion chelated on the microspheres (546 μmol Cu(II)/g), and they were used in the invertase adsorption. Maximum invertase adsorption was 51.2 mg/g at pH 4.5. Cu(II) chelation increases the tendency from Freundlich-type to Langmuir-type adsorption model. The optimum activity for both free and adsorbed invertase was observed at pH 4.5. The optimum temperature for the poly(HEMA-VIM)/Cu(II)-invertase system was found to be at 55 °C, 10 °C higher than that of the free enzyme at 45 °C. V _max values were determined as 342 and 304 U/mg enzyme, for free and adsorbed invertase, respectively. K _m values were found to be same for free and adsorbed invertase (20 mM). Thermal and pH stability and reusability of invertase increased with immobilization.